1. Field of the Invention
The present invention is directed to a radiological system wherein x-ray images (radiation images) can be produced and displayed on a display monitor, the radiation images being converted into video images through a video chain which exhibits a predetermined modulation transfer function.
2. Description of the Prior Art
As is known, the function of an imaging system (video chain) in the context of a radiological system is to translate the modulation of the x-ray beam into a visible image and to reproduce this modulation faithfully, so that the features of the imaged object are apparent. The ability of an imaging system to fulfill this responsibility is known as the modulation transfer function. The modulation transfer function of the composite system is the product of the respective modulation transfer functions of the individual components of the system.
In radiological systems of the type described above, the influence of the ambient luminosity in the environment of the screen of the video monitor, for example, a television monitor, can be reduced by the use of anti-reflective coatings on the picture screen surface of the monitor, by coloring the monitor glass, and/or by controlling the contrast or brightness dependent on the ambient luminosity. These measures enable a high ambient luminosity to be present at the picture screen, however, this may have a disadvantageous influence on the modulation transfer function at the picture screen. High changes in illumination can also disadvantageously affect the modulation transfer function at the picture screen. As noted above, the modulation transfer function in radiology is a measure, among other things, of the extent to which contrasts in the radiation image (i.e., the invisible radiation image produced by x-rays penetrating a subject) are transferred into the visual image, these contrasts being dependent, in part, on the size of the details in the radiation image.